Mindfulness meditation takes meditation into your daily life so you can learn to catch yourself running around like a stressed squirrel, anwering the phone on the first ring, running to the photo copier, etc. Learn to watch yourself at all times. Try moving slowly when washing your hair, putting away dishes, folding clothes. This all helps to move you from sympathetic dominance.
Magnesium can help calm your nervous system. After years of chronic stress, your cells will be low on Mag for sure. Magnesium oil is the most efficient way to get it into your blood stream. Just don't over do it.
You can also try some things like Valerian, Ashwaganda.
Stay away from stimulants like Rhodiola, Ginseng. Anything that gives you more energy immediately will likely cause a crash.